Mammography system and method employing offset compression paddles, automatic collimation, and retractable anti-scatter grid

ABSTRACT

A mammographic imaging system is optimized for use with a single fixed size flat panel digital image receptor. It accommodates compression devices (paddles) of varying sizes, and positions them properly in a field of view of the image receptor. When a compression paddle with size smaller than the field of view of the image receptor is used, the compression paddle can be shifted laterally in the direction parallel to the chest wall, so as to facilitate different views of different size breasts, and permit the image receptor to image as much of the desired tissue as possible. An automatic X-ray collimator restricts the X-ray illumination of the breast in accordance with the compression paddle size and location in the field of view. An anti-scatter grid, mounted inside the image receptor enclosure, just below the top cover of the enclosure, can be retracted out of the field of view of the image receptor for use in magnification imaging.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application No.14/595,826, now abandoned, filed Jan. 13, 2015, which is a continuationof U.S. patent application No. 14/052,825, now U.S. Pat. No. 8,948,340,filed Oct. 14, 2013, which is a continuation of and claims priorityunder 35 U.S.C. § 120 to U.S. patent application Ser. No. 13/190,989,now U.S. Pat. No. 8,559,595, filed Jul. 26, 2011, which is acontinuation of U.S. Pat. No. 7,986,765, filed on Feb. 22, 2010, whichis a continuation of U.S. Pat. No. 7,688,940, filed on May 8, 2009,which is a continuation of U.S. Pat. No. 7,609,806, filed Jan. 15, 2008,which is a continuation of U.S. Pat. No. 7,319,735, filed Nov. 30, 2006,which is a continuation of U.S. Pat. No. 7,443,949, filed Oct. 18, 2004,which is a Section 371 national stage of International Application No.PCT/US02/33058, filed Oct. 17, 2002, claiming the benefit of U.S.Provisional Application No. 60/350,213, filed Oct. 19, 2001. Each of theabove applications is hereby incorporated by reference.

BACKGROUND

X-Ray mammography machines typically use an x-ray source mounted at oneend of a rotatable c-arm assembly and an image receptor at the other.Between the x-ray source and the image receptor is a device forcompressing and immobilizing a breast. Until recently, the imagereceptor was typically a screen-film (s/f) cassette, which generated animage related to the detected transmission of x-rays through the breast.These s/f cassettes typically come in standard sizes, e.g., 18 cm×24 cm(small) and 24 cm×30 cm (large), with the large cassette used when thebreast is too large to be uniformly compressed by the small cassette.The cassettes are easily attachable and removable from a breast supporttray of a conventional mammography system. The device for compressingthe breast is often called a paddle, and comes is a variety of sizes tomatch both the cassette size and the breast size. Such matching isdesirably because the use of a small size paddle on a large breast canresult in uneven and inadequate breast compression and may not allowfull-breast imaging, which using a large paddle on a small breast canimpede access to the breast, which is important during the compressioncycle in order to optimize the amount of breast tissue brought into thefield of view of the image receptor.

New mammography systems are now being developed to use digital imagereceptors as replacements for the screen-film cassettes. These digitalimage receptors, sometimes called flat panel receptors, or flat paneldigital x-ray receptors, are different in many ways from s/f cassettes.They have many advantages, but also tend to be heavier and somewhatthicker. Typically, they are not designed to be removed in normal use,so a system normally will employ only one size image receptor. Thesecharacteristics can presents challenges for some imaging procedures andbreast sizes, particularly for the mediolateral oblique view (MLO) takenas a part of typical breast x-ray imaging. As with screen-film system,it is still advantageous to use a compression paddle that matches thebreast size. This typically means that the compression paddles will beremovable, and there will be a selection of paddle sizes available withthe system.

A number of x-ray protocols have been used for breast imaging. Onecommon view is the cranio-caudal (CC) view, illustrates in FIG. 5, whichimages the breast of a standing or sitting patient from above. Anotheris the mediolateral oblique view (MLO), taken from an oblique or angledview, and also illustrated in FIG. 5. In screen-film mammographysystems, the compression paddle typically is centered relative to theproximal edge of the screen-film cassette. In some views, such as theMLO view, and particularly for smaller breasts, this may present somedifficulty as the cassette may have to be pressed against the armpit inorder to approximately center the breast relative to the proximal edgeof the film (the edge closest to and parallel to the chest wall). Insuch cases, the smaller size cassette can be used. This, plus therelative thinness of the cassette, generally allow for adequatecentering. However, when a digital x-ray receptor is used usually onlyone size is available, and it may be the size comparable to the largersize screen-film cassette. Also, the digital receptor tends to bethicker than a screen-film cassette. Thus, centering the breast can bedifficult or impossible in some cases, particularly for the MLO view andpatients with smaller breasts, with the result that optimal positioningof the breast may not be possible for some views and patients.

To applicants' knowledge, these and other issues regarding compressionpaddle use with flat panel digital receptors in mammography have notbeen solved and perhaps have not been even addressed. In a differentsetting, it has been proposed to move a compression paddle laterally,relative to the proximal edge of the screen-film cassette, but for thedifferent purpose of aligning a cutout in the paddle with a particularportion of the breast. See U.S. Pat. No. 5,199,056. This is believed torequire a paddle larger that would normally be used for the breast sizeso as to maintain even compression when the cutout is off-centerrelative to the breast. Other earlier proposals are know for featuressuch as collimation that adjusts to film cassette size, source-to-imagedistance and/or cross-sectional area to be imaged (U.S. Pat. Nos.3,502,878, 3,863,073, 5,627,869, and 6,149,301), moving a paddle (U.S.Pat. No. 3,971,950), moving a cassette (U.S. Pat. No. 4,989,227), andretracting a cassette holder (U.S. Pat. No. 4,559,641). The citedpatents are hereby incorporated by reference in this patentspecification.

SUMMARY

An object of the disclosed system and method is to provide mammographythat overcomes known disadvantages of proposals involving the otherwisedesirable use of flat panel, digital x-ray receptors.

Another object is to employ compression paddles that match both the sizeand position of the patient's breast relative to the proximal edge of adigital x-ray image receptor so as to improve image quality, patientcomfort and the ability of the health professional to position thebreast optimally for imaging.

Another is to provide automated collimation control that changes x-raybeam collimation in accordance with one or more of the size and positionof the compression paddle and of the breast, and the position of abreast platform relative to the receptor, preferably in response toinformation that is automatically sensed.

Another is to provide x-ray exposure control that is responsive to atleast one of the size and position of the compression paddle, theposition of the breast, and a pre-exposure x-ray measurement, preferablyin response to information that is automatically sensed.

Another is to provide a scatter-suppression grid that is retracted forimage magnification protocols, preferable automatically in response tosensing a breast position for magnification imaging.

These and other objects are met in a non-limiting example comprising amammography system having a flat panel digital x-ray receptor, an x-raysource selectively emitting a collimated x-ray beam toward the receptor,and a compression paddle of a selectable size mounted for selectivemovement at least along a proximal edge of the x-ray receptor as well asalong the x-ray beam. At least for selected breast x-ray protocols, apatient's breast is positioned off-center relative to the proximal edgeof the x-ray receptor, and paddle of an appropriate size also ispositioned off-center relative the same proximal edge to compress thebreast for x-ray imaging.

In addition, the system includes one or more of a number of otherfeatures. An exposure control can be responsive to information regardingbreast thickness along the beam direction to control x-ray exposure forimaging. This information can come from a conventional auto-exposuresensor (AES) resulting from a pre-exposure, low-dose firing of the x-raysource from an output of the digital x-ray receptor during suchpre-exposure firing, and/or from sensors for the relative positions ofthe x-ray source, the x-ray receptor, the compression paddle and/or thebreast tray. The system can include a collimation control responsive toinformation regarding one or more of the size of the paddle, itslocation along the beam, its location relative to the proximal edge ofthe receptor, a desired field of view, magnification parameters, and thelike. This information can come from appropriate sensors and/or can beinput by the health professional carrying out imaging. The system caninclude a scatter-suppressing grid selectively movable between aposition in the path of the imaging beam and a position outside the path(for magnification imaging). Again, information for controlling gridposition can come from one or more different sources. And, the systemcan include a built-in or a separate viewing station receiving x-rayimage information from the x-ray receptor and possibly from some or allof the sensors, processing it, and displaying the results as an imageand/or in other forms.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 illustrates a partial side view of a mammography system imaging apatient's breast.

FIG. 2 illustrates the system also in side view but in more detail andin a magnification mode.

FIG. 3 illustrates a lateral displacement of a small compression paddlealong the proximate edge of the image receptor.

FIGS. 4A, 4B, and 4C show three common positions of a small compressionpaddle relative to the image receptor.

FIG. 5 illustrates two common x-ray protocols for breast imaging.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIG. 1, an x-ray source 1 is at one end of a generallyC-shaped frame 7 and a flat panel digital x-ray imaging receptor 5 is atthe other end. X-ray source 1 includes a collimator schematicallyillustrated at 40 to confine an x-ray beam 30 emitted from source 1 to adesired footprint at receptor 5, typically no larger than the area ofreceptor 5 and preferably just enough to image a patient's breast 3 orat least a selected part thereof, as compressed toward receptor 5 by acompression paddle 2 mounted on an arm 6 that in turn mounts to frame 7.A lower platform 11, often called a breast tray, is immediately belowthe breast, and a scatter-reducing grid 4 is between breast tray 11 andx-ray receptor 5 and is housed in the same enclosure 12 with thereceptor. As is known in the art, frame 7 can rotate between horizontaland vertical direction of x-ray beam 30.

In use for a CC view, paddle 2 and its supporting arm 6 are moved up,breast 3 is positioned on tray 11 and compressed by bringing paddle 2down as needed. With suitable collimation by collimators 40 (whichtypically collimate in two directions, of which only one is illustratedin FIG. 1), beam 30 from source 1 images the breast onto receptor 5 andthe resulting electronic image information is transmitted to a viewingstation 22 (FIG. 2). The image typically is rectangular. Preferably, thecollimation is such that beam 30 illuminates an area of receptor 5 justlarge enough to show the image of breast 3, or at least a selected partthereof. Importantly, different sizes and shapes of paddles 2 can bemounted to arm 6, and the paddle can be selectively positionedoff-center relative to proximal edge 5 a of receptor 5 (the left edge inFIG. 1).

Referring to FIG. 2, the system can operate in a magnification mode inwhich the relative positions along x-ray beam 30 of source 1, breasttray 11, and/or receptor 5 are adjusted to provide the desired imagemagnification. In this example, source 1 and receptor 5 stay in placebut tray 11 slides up support 7 to a position spaced up from receptor 5,and the collimation of beam 30 is adjusted as needed. Note that formagnification imaging scatter-reducing grid 4 is withdrawn from theportion of receptor 5 that receives the desired breast image, becausethe angles of the grid septa typically are not suitable for amagnification view. If these angles can be changed to match the selectedmagnification, the grid can remain in place. Alternatively and ifdesired, a different grid that is suitable for the selected magnifiedview can be introduced in place of grid 4 in FIG. 1. Auto-controls 1 acan include (a) an auto-exposure control coupled with an AEC sensor 24and/or receptor 5 to receive exposure information in a pre-imagingfiring of source 1, (b) an auto-collimation control to adjust thecollimation of beam 30, (c) an auto-grid control to selectively withdrawgrid 4, and (d) an auto-magnification control to adjust parameters formagnification imaging. AEC sensor 24 can be conventional separate sensorthat helps determine imaging exposure parameters in a pre-imagingexposure of the immobilized breast at a low x-ray dosage. Alternatively,receptor 5 can be used for that purpose, eliminating the need for aseparate AEC sensor, because the output of receptor 5 resulting from alow-dose pre-imaging exposure can provide the information forauto-exposure control. In addition, the output of receptor 5 in responseto the pre-imaging exposure can reveal the position of the breastrelative to the receptor, and thus provide information forauto-collimation to confine beam 30 to a footprint that matches thebreast even when the breast is off-center relative to proximal edge 5 a.The auto-collimation control can be an arrangement sensing size and/orthe position of one or more of breast 3, paddle 2, and tray 11, usingrespective sensors and automatically adjusting collimators 40 to confinebeam 30 to the required cross-section and position. The auto-gridcontrol can respond to a signal indicating that that magnificationimaging will be carried out to withdraw grid 4, for example to theposition shown in FIG. 2, using a motor 4 a. This signal can come frominformation provided by respective sensors or it can be input by thehealth professional using the system. The auto-magnification control canbe an arrangement responding the data entered by a health professionalthrough viewing station 22, or in some other way, e.g., based oninformation from sensors to adjust the system elements involved inmagnification. Information for the auto-controls can be provided invarious ways. One is from sensors S that keep track of the size andposition of paddle 2 along beam 30 and relative to proximal edge 5 a ofx-ray receptor 5, of the position of breast tray 11 along beam 30, ofthe position of grid 4, and the setting of collimators 40. Another isinputs from an auto-exposure sensor and/or x-ray receptor 5 resultingfrom a pre-exposure firing of beam 30 at low dose, with breast 3 inplace for imaging. As is known in the art, the output of receptor 5 canbe used to detect the position of breast 3 relative to receptor 5, or atleast the approximate position of the breast relative to proximal edge 5a. Yet another possible source of information for the auto-controls isinputs from the health professional using the system, through a keyboardor other input devices in viewing station 22 or elsewhere. Informationis exchanged between auto-controls 1 a, sensors S, and viewing station22 over appropriate links, shown schematically. Suitable arrangements,including encoders, motors (of which only motor M retracting andrestoring grid 4 is expressly illustrated), and other control elementsare included in mammography system 10 but, for clarity of the drawings,are not expressly illustrated.

FIG. 3 illustrates an example of an arrangement for positioning paddle 2off-center relative to proximal edge 5 a of receptor 5. While suchoff-center positioning can be used for other views as well, it is mostimportant for views such as the MLO view. As seen in FIG. 3, paddle 2includes a rib 20 that has a channel slot 20 a and is secured to arm 6with a removable and adjustable lock or detent 21 that passes throughchannel 20 a. In operation, the health professional selects a paddle 2that is suitable in size and perhaps in shape to the breast to beimaged, removes any existing paddle 2 from arm 6 by pulling out orunscrewing detent 21, and installs the selected paddle 2 by securing itto arm 6 with detent 21 in a position relative to proximal edge 5 a thatmatches the patient's breast's position. Any desired further lateraladjustment can be made by sliding paddle 2 along the direction of theproximal edge 5 a, before or during compressing the breast for taking animage.

FIGS. 4a, 4b, and 4c illustrate an alternated arrangement for lateraladjustment of paddle 2. Here a paddle 2 of a selected size and possibleshape is removable secured to arm 6, and arm 6 is in turn slidablysecured to frame 6 to slide laterally, along the direction of proximaledge 5 a of receptor 5. The term “lateral” is used here to designatemovement parallel to, or at least generally along, the proximal edge 5a, even when the imaging plane of receptor 5 is oriented for an MLO viewor is vertical. For example, FIG. 4 can illustrate a position of paddle2 for an MLO view of the left breast, FIG. 4b can illustrate a positionfor a CC view, and FIG. 4c can illustrate a position for an MLO view ofthe right breast.

It should be clear than many other arrangements and variations will beapparent to persons skilled in the technology based on the disclosure inthis patent specification and that the above embodiments are only someof examples embodying inventions whose scope is defined by the appendedclaims.

The invention claimed is:
 1. A mammography system comprising: a flatpanel digital x-ray receptor having a proximal edge relative to apatient's breast to be imaged; and a compression paddle operably coupledsuch that the compression paddle moves generally along the proximal edgeof the receptor, wherein the compression paddle is configured to bepositioned in a first position substantially centered along a length ofthe proximal edge of the x-ray receptor, and a second positionoff-center relative to the x-ray receptor.
 2. The system of claim 1,wherein the compression paddle is configured to slide between the firstposition and the second position.
 3. The system of claim 1, wherein thecompression paddle is secured in at least one of the first position andthe second position with an adjustable lock.
 4. The system of claim 1,wherein the compression paddle is secured in at least one of the firstposition and the second position with a detent.
 5. The system of claim4, wherein the compression paddle includes a channel to facilitatemovement of the compression paddle relative to the x-ray receptor. 6.The system of claim 1, wherein the second position that is off-centerrelative to the x-ray receptor is for an MLO view of the patient'sbreast.
 7. The system of claim 1 further comprising a scatter-reducinggrid removably positioned between the compression paddle and the x-rayreceptor.
 8. The system of claim 7, wherein the scatter-reducing grid isin a first position for a first imaging mode and in a second positionfor a second imaging mode.
 9. The system of claim 8, wherein thescatter-reducing grid is not positioned between the compression paddleand the x-ray receptor for the second imaging mode.
 10. The system ofclaim 9 further comprising a motor coupled with the scatter-reducinggrid for moving the grid between the first position and the secondposition.
 11. The system of claim 1 further comprising an exposurecontrol responsive to information regarding at least one of the one ormore positions of the compression paddle.
 12. A method of imaging apatient's breast with a mammography system comprising: providing a flatpanel digital x-ray receptor having a proximal edge relative to apatient's breast to be imaged; securely positioning a compression paddlealong a length of the proximal edge of the x-ray receptor, thecompression paddle operably coupled such that the compression paddlemoves generally along the proximal edge of the receptor, wherein thecompression paddle is configured to be positioned in a first positionsubstantially centered along a length of the proximal edge of the x-rayreceptor, and a second position off-center relative to the x-rayreceptor; compressing the patient's breast between the x-ray receptorand the compression paddle when the compression paddle is in the firstposition; and imaging the patient's breast with x-rays from an x-raysource.
 13. The method of claim 12, wherein securely positioning thecompression paddle includes sliding the compression paddle between thefirst position and the second position.
 14. The method of claim 13,wherein the compression paddle is secured in at least one of the firstposition and the second position with an adjustable lock.
 15. The methodof claim 13, wherein the compression paddle is secured in at least oneof the first position and the second position with a detent.
 16. Themethod of claim 12 further removably positioning a scatter-reducing gridbetween the compression paddle and the x-ray receptor.
 17. The method ofclaim 16, wherein the scatter-reducing grid is in a first position for afirst imaging mode and in a second position for a second imaging mode.18. The method of claim 17, wherein the scatter-reducing grid is notpositioned between the compression paddle and the x-ray receptor for thesecond imaging mode.
 19. The method of claim 17, wherein a motor coupledwith the scatter-reducing grid moves the grid between the first positionand the second position.
 20. The system of claim 1, wherein when in thesecond position, an edge of the compression paddle is substantiallyaligned with an edge of a breast support platform.